1. Field of the Invention
This invention relates to a camera positioning system, typified by a stationary mounted camera having an adjustable field of view. The camera""s field of view may be changed via pan, tilt, or zoom operations. Of particular relevance to this invention are cameras which are mounted adjacent a stationary plane, such as a wall or ceiling, and which have zoom capability.
2. Description of Related Art
Commercial security systems often comprise security camera systems. The camera system typically comprises a camera having a magnification (zoom) capability, mounted upon a platform which can rotate in a horizontal plane (pan), and in a vertical plane (tilt). The operator is provided with means for effecting the pan, tilt, or zoom operations, typically via rocker switches associated with each operation. The pressing the switch at one end effects a movement in one direction, the pressing of the switch at the other end effects a movement in the opposite direction. Other adjusting means, such as joysticks, are also common, such systems also often provide an ability for automation, a continuous scan of an area, or a directed adjustment to a particular area in the event of an alarm.
Typically, the placement of the security camera system is chosen to be at a non-obtrusive location, such as mounted in a ceiling or wall fixture. The fixtures are designed to be non-obtrusive as well, extruding as little as possible from the ceiling or wall. Because of this placement, the effective field of view of the camera is bounded by the ceiling or wall, even though the span of movement of the camera (pan, tilt) or the camera""s lens (zoom) may extend beyond the ceiling or wall. Conventional systems often contain pan and tilt xe2x80x9cstopsxe2x80x9d to prevent the operator from adjusting the camera to beyond the ceiling or wall. Such stops are sets to limit the camera rotation in the horizontal or vertical direction, ideally in such a way so that the extreme of the camera""s view angle is coincident with the ceiling or wall.
Because the camera""s view angle is dependent upon the magnification, or level of zoom, of the camera, the coincidence of the extreme of a camera""s view and the ceiling or wall will only occur at a particular level of zoom. Views at a lower level of zoom will result in a wider camera view angle, and thus include more of a view of the ceiling or wall. The included view of the ceiling or wall results, in effect, in a reduced view of the secured area, because the view of the ceiling or wall contains no useful security information. Views at a higher level of zoom will result in a narrower camera view angle, thus eliminating the view of the scene between the ceiling or wall and the extreme of the narrower camera view angle. The latter case presents a potential security flaw, by producing a void, or blind spot, in the secured area; for this reason, the stop is typically set when the camera is at the highest level of zoom. Thereafter, the view of the scene adjacent to the ceiling or wall will result in the aforementioned loss of useful viewing area at all other levels of zoom.
It is an object of this invention to optimize the viewing area of a camera system by minimizing the inclusion of bounding areas, such as ceilings and walls, in said viewing area, at all angles of view of the camera. This object is accomplished by suitably adjusting the line of sight of the camera in dependence upon the camera""s angle of view, and in dependence upon the location of the bounding area relative to the camera""s line of sight and angle of view.
Depending upon the degree of optimization required, the appropriate adjustment can be determined algorithmicly or empirically. Algorithmic means can be provided to appropriately adjust the camera""s line of sight by employing a two or three dimensional model of the camera""s field of view within its situated environment. Empirically, the adjustment can be determined by positioning the camera such that the view is optimized at varying angles of view, storing the parameters of the optimized views, and subsequently determining the adjustment required at other angles of view based upon an interpolation of the stored parameters.